Borehole treatment agents are all types of auxiliary liquids which can be used in the drilling for crude oil or natural gas deposits. So called drilling liquids and drilling muds or drilling fluids built up thereon, which can be used both in land-based and in sea-based bores, are particularly important in this regard. On the one hand water-based drilling fluids are known which have a content of about 1 to 50% of emulsified oil phase—in addition to the other conventional auxiliary substances of a drilling fluid of this type—and which are also referred to as O/W emulsion fluids (oil-in-water emulsions). On the other hand, broadly oil-based fluid systems, in which the oil forms the free-flowing phase or at least a substantial portion of the free-flowing phase as a closed oil phase, are in practical use. So called invert drilling muds, which on the basis of W/O emulsions (water-in-oil emulsions) comprise a disperse, aqueous phase in the closed oil phase, are particularly important in this regard. The content of disperse, aqueous phase is conventionally in the range of from at least about 5 to 10% by weight to about 50 to 60% by weight. However, also known in addition to these W/O invert drilling muds are so called true oil muds, the liquid phase of which is formed almost exclusively from a closed oil phase, comprising in dispersed form at most small amounts—conventionally not more than about 5 to 10% by weight—of aqueous phase.
The non-aqueous phase of fluid systems of this type is formed by what is known as the carrier fluid. The carrier fluid is originally diesel oil which, mixed with specific additives, forms the actual drilling fluid. However, the end of the 1980s saw a demand for environmentally friendly fluid systems and thus environmentally friendly carrier fluids.
These were intended to be in particular more biodegradable than the previously used diesel oil.
In addition to a wide range of liquid esters, such as are described for example in EP-A-374 672, the usability of olefinic hydrocarbons and paraffins was also examined. Reference may be made in this regard by way of example to EP-A-0 765 368 which relates to the use of so called α olefins as a carrier fluid.
Drilling fluids for geological exploration are in practice dispersions made up of a liquid and a solid phase, the drilling fluid having a significant solids content. Such dispersions are liquid flushing systems for sinking rock bores, bringing up the loose drillings. It is therefore necessary for the drilling fluids to have a specific density (generally greater than 1.2 g/cm3, preferably greater than 1.5 g/cm3) so as to be able to prevent any collapse of the formation. For this purpose, solids are added to the fluid for weighting. Barium sulphate is generally used. Under shear loads, solids-comprising liquids of this type generally display thixotropic behavior, i.e. the viscosity of these systems, which are also referred to as non-Newtonian liquids, decreases under the influence of increasing shear stress or shear rate. In practice, this behavior can then lead to problems when the liquids are to be transported or pumped and are in the process subjected to different mechanical loads.
In addition to thickeners, drilling fluids generally also comprise viscosity modifiers in order to optimize the viscosity behavior of the drilling fluids for the particular area of application, in particular the use of hydrophobized bentonites as viscosity modifiers in drilling fluids being known in the art. In this regard, it should be borne in mind that marked thickening and thus reduced pumpability can occur in drilling fluids comprising hydrophobized bentonites of this type as viscosity modifiers, in particular in deep bores, partly on account of the very high temperatures prevailing there. This has an adverse effect inter alia on the machinery, in particular on the pumps and running times. A further aim is to keep the solids content as low as possible, in particular in very deep bores.
The present invention was based on the object of overcoming the drawbacks resulting from the prior art in relation to drilling fluids.
In particular, the present invention was based on the object of disclosing an additive which is as liquid as possible and is suitable as a thickening agent in drilling fluids, in particular in oil-based drilling fluids, so that if appropriate solid-type thickening agents or viscosity modifiers in drilling fluids may be dispensed with, but at least the amount thereof may be significantly reduced. In this case, the additive should not only display good thickening properties, but should in addition be as biodegradable as possible, so that a use of a drilling liquid comprising an additive of this type is advantageous from an ecological perspective as well. The additive should also impart an improved lubricating effect to the drilling fluid.
In addition, it should be possible to produce the above-described, advantageous additives as cost-effectively as possible compared to the additives used as a thickening agent in the prior art.
The present invention was also based on the object of disclosing a composition which is suitable as a drilling fluid, wherein this composition should have a solids content which is as low as possible. It should also be possible to use this composition as a drilling fluid in a spectrum which is as broad as possible, but in particular both in onshore and in offshore bores, above all there in deep sea bores. In addition, the drilling fluid should be distinguished by advantageous, ecotoxicological behavior, be as biodegradable as possible and be able to be produced from starting materials which are as inexpensive as possible.